Accelerated development of a safe and easily manufactured Q fever vaccine

Q fever is an important and highly contagious disease of worldwide importance affecting both livestock and humans caused by the intracellular Gram-negative bacterium, Coxiella burnetii. Infection of humans occurs following exposure to as few as 1-10 bacteria and can result in both acute and chronic forms of disease. Infections can result in death, especially in the elderly or immunocompromised. Livestock, in particular sheep and goats, are the major source of human infections where infection can cause abortion, stillbirth and delivery of weak offspring. The loss of lambs and kids can result in devastating economic losses to the livelihoods of farmers in Europe as well as LMIC countries, particularly during abortion storms where up to 35% losses can occur.

Vaccines are currently considered the most effective way to control Q fever, and vaccines based on inactivated C. burnetii organisms are commercially available for use in both ruminants and humans. However, the safety of these vaccines is a major issue considering that severe local and systemic reactions occur post-vaccination in humans previously exposed to the bacteria and vaccination of ruminants is associated with significant production losses. Furthermore, manufacture of these vaccines involves culture of the organisms, which has both cost and safety issues. These issues have resulted in limited use of these vaccines. There is therefore an urgent need to develop safe, effective and easily manufactured vaccines to control Q fever in both humans and livestock species.

To this end, attempts have been made to develop subunit vaccines targeting key C. burnettii proteins which would be safer to manufacture and could be engineered to induce fewer side effects following vaccination. However, current approaches to subunit vaccine development have been severely hampered by a lack of knowledge of the appropriate bacterial proteins to target.

In this project, we will use novel peptide chip array technology to identify the key C. burnetii proteins recognised by antibodies from sheep and goats vaccinated with the current protective, but unsafe commercial vaccine in a high throughput and detailed manner. These antibody responses will be compared with those generated by a non-protective C. burnetii vaccine which is based on a different (non-virulent) form of the bacteria. By comparing antibody responses from protected and non-protective vaccines, bacterial proteins which are specifically targeted by the protective vaccine will be identified. Synthetic versions of these proteins will then be generated and subunit vaccines based on pools of these proteins will be tested in a sheep challenge model. This will provide preliminary safety and efficacy data to inform future Q fever vaccine development programmes.

Q fever vaccines based on formalin inactivated phase I C. burnetii are protective but have considerable safety issues, both in terms of their manufacture and post-vaccination reactions. Vaccines based on the avirulent inactivated phase II C. burnetti are safer but non-protective. The aim of this project is to identify C. burnetii protein antigens which contribute to the protection induced by the phase I vaccine in order to rationally design a safe subunit Q fever vaccine.

To do this we will use novel high-density peptide chip arrays representing all open reading frames of the C. burnetii vaccine strain (strain RSA493) in 15-mer overlapping peptides. Pooled serum from sheep and goats vaccinated with the phase I vaccine will be used to probe peptide chips to identify antibody reactive peptides. Positive peptide hits from pooled serum samples will be validated at the individual animal level by ELISA using individual peptides. Pooled serum samples from sheep vaccinated with the phase II vaccine as well as samples from sheep, goats and humans exposed to C. burnetii will also be examined to identify peptides which are uniquely recognised by serum from individuals vaccinated with phase I but not phase II vaccines, and those unique to serum from exposed individuals (potential DIVA targets).

Once we have identified a panel of peptides which are associated with the protective vaccine, we will infer the protein target of peptide by comparison with the C. burnetii strain RSA493 genome, and select proteins which are recognised by all phase I vaccinated individuals. Proteins will be further selected based on known importance for C. burnetii virulence-related functions and sequence conservation between C. burnetii strains. The final pool of proteins will be synthesised as E. coli recombinant proteins. Prototype vaccines based on pools of these recombinant proteins will be tested for safety, immunogenicity and efficacy in a pregnant sheep C. burnetii challenge model.

Who might benefit from this research?

At sequential stages of the project, scientists involved in vaccinology; commercial and non-profit vaccine manufacturers and distributors in developed countries and Low to Middle Income Countries (LMICs); livestock producers and meat industry workers (veterinarians, farmers, stockmen, dairymen, abattoir workers, animal transport workers, animal traders) in developed countries and LMICs worldwide; populations of humans living in close proximity to animals where agriculture and animal husbandry are significant sources of income.

How might they benefit from this research?

Scientists involved in vaccinology will benefit directly from the novel approach to antigen identification and will receive novel information on these processes via our Pathways to Impact, which may have direct downstream impact on their approach to vaccine production for a range of other viral, bacterial and multi-cellular pathogens. Vaccine manufacturers and distributors will benefit by having a safe, effective, easy to manufacture product which is also easy to store and administer. Coxiella burnetii infection in domesticated livestock has been associated with abortions, especially in sheep and goats, and infertility in cattle and therefore can have a profound economic impact on production worldwide[1]. The availability of a novel, cost-effective and protective vaccine for use in animals therefore benefits livestock producers but also helps to protect veterinary and agricultural workers by limiting their exposure to the pathogen, resulting in increased productivity and quality of life [2]. The potential public health benefits of an effective livestock vaccine can be illustrated by the 2007-2010 Q fever epidemic in the south-east Netherlands where >3000 cases of Q fever were notified in that short period. In this scenario, only ~3% of patients worked in the agricultural sector and only 0.5% worked in the meat-processing industry but the geographical area of the epidemic was densely populated and intensively farmed with dairy goats, resulting in the suspected transmission of contaminated dust from Coxiella-infected goats to humans living close-by [3]. Control measures including mandatory vaccination and culling on infected farms brought the epidemic to an end.

References
[1] Stark et al. Schweizer Archiv fur Tierheilkunde 139, 343-353.
[2] Kermode et al., Aust N Zealand J Public Health, 27, 390-398.
[3] Dijkstra et al. Immunol Med Microbiol 64, 3-12.